Conventionally, plastics have characteristics such as processability and usability, whereas, they have been thrown away after use owing to their difficulty in recycling, and to hygienic point of view. However, as the use and disposal of the plastics increase, problems associated with their disposal by landfilling or incineration have drawn attention, and they may be responsible for great burden on the global environment such as deficiency of garbage landfill site, influences on ecological system by remaining nondegradable plastics in the environment, generation of detrimental gas in combustion, global warming resulting from a large amount of combustion calorie, and the like. In recent years, biodegradable plastics have been extensively developed as a material which can solve the problems of the plastic waste.
Additionally, these biodegradable plastics are of plant origin, and absorb and fix carbon dioxide in the air. Carbon dioxide generated in combustion of these biodegradable plastics of plant origin was originally present in the air, therefore increase in carbon dioxide in the atmosphere is not caused. This phenomenon is referred to as “carbon neutrality”, which tends to be placed importance thereon. Carbon dioxide fixation is expected to be effective in preventing the global warming. Particularly, in connection with Kyoto Protocol in which achievement level of carbon dioxide reduction was suggested, deliberation of Congress for ratification was approved in Russia in August 2003. Therefore, it is highly probable that the Protocol will come into effect actually, whereby materials for carbon dioxide fixation have drawn a great deal of attention, and active use thereof has been desired.
Meanwhile, although aromatic polyesters have been produced and consumed in large quantities as general-purpose polymers, in light of fixation of carbon dioxide and prevention of global warming, they are not preferable material in terms of the carbon neutrality, because they are produced from fossil fuels, thereby leading to release of carbon dioxide fixed in the ground to the atmosphere. For example, Patent Document 1 describes that addition of a highly dispersible high-molecular weight vinyl aromatic copolymer to an aromatic polyester enables enhancement of the melt strength. However, as described above, this polyester resin composition is not a preferable material in light of the carbon neutrality.
Accordingly, in light of the carbon neutrality, aliphatic polyester-based resins, particularly polylactic acid-based resins, poly(3-hydroxyalkanoate), more particularly poly[(3-hydroxybutyrate)-co-(3-hydroxyhexanoate)] and the like have been drawn attention as the plastics of plant origin.
However, these resins are problematic in terms of physical properties and molding processability in use without modification. For example, Patent Document 2 describes a thermoplastic resin composition including a graft copolymer prepared using a polylactic acid-based resin, and a polyorganosiloxane/acrylic composite rubber containing polyorganosiloxane and an alkyl (meth)acrylate rubber. However, physical properties, particularly impact resistance and transparency of the resin composition are not enough.
In addition, poly(3-hydroxyalkanoate) copolymers that are biodegradable aliphatic polyester-based resin exhibits significant draw down during melt processing in extrusion molding or vacuum molding, while weld flash is likely to be generated in injection molding. Therefore, improvement of these disadvantages was required.
Moreover, Patent Document 3 describes that molding processability in vacuum molding, air-pressure molding and the like can be improved by compounding an acryl compound to polyester that is a thermoplastic polymer. However, a (3-hydroxyalkanoate) copolymer that is a biodegradable aliphatic polyester-based resin is not referred to as the polyester.
Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei 6-41376;
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-285258;
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-155207;